Concentrating chromite ores by froth flotation



Sept. 17, 1935. W 2,014,40fi1 CONGENTRATING CHROMITE ORES BY FROTH FLOTATIYON Filed Oct. 12, 1952 On Concenirate Coarse Crushers Wa'le r BallnrRod F Mill Classifier Water m Desliming Sand Classifier 50 Oleic Acid to neutral Dispersion Conditi'onin r e Cell 2 5,," H 50 Rod io pH 6.0

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Ta Tails Thickener Filter m A Tails l l Discard Water T n INVENTOR FLOYD Y WEE BY Q M A'ITORNEYS Patented Sept. 17, 1 935 I PATENT OFFICE CONGENTRATING CHROMITE ORES BY FROTH FLOTATION Floyd Weed, Jefl'erson City, Tenn. 7

Application October 12, 1932, Serial No. 637,527

' 30 Claims. (01. 209-166) This invention relates to methods of ore concentration and more particularly to methods of ore concentration by froth flotation; Still more particularly this invention relates to methods of concentrating chromium ores and more specifically chromite ores by froth flotation.

Heretofore in the art these ores have been concentrated by mechanical means or by means utilizing the differences in specific gravitiesor 'electrical' characteristics of the chromite and the gangue'. In low grade ores such methods of concentration are commercially impractical. Heretofore many attempts have been made to concentrate chromium containing ores and in particular chromite ores by flotation methods but such methods as have heretofore been proposed have either been commercially impractical or have involved the use of such relatively large quantities of reagents that the application of the same to other than high grade chromite ores has been impractical.

One of the objects of the present invention is to provide a simple and economical process for the concentration of chromium containing ores Still another object of the present invention is to provide an improved reagent for use in the froth flotation of chromite ores.

Other objects and advantages will become apparent as the invention is more fully disclosed.

Heretofore in the art in the froth flotation of non-sulfide ores, it has been found that the fatty acids of the saturated and unsaturated series exert a selective aflinity for the metal values of the ores. The chief difllculty heretofore encountered is to properly incorporate the fatty acid with the ore so that efficient results may be obtained. It has heretofore been proposed to dissolve the fatty acid in a suitable solvent such as alcohol and to add this solution to the flnely ground ore or to the flotation pulp. It has also been proposed to combine the fatty acid with suitable bases to 'form water soluble soap compounds which are added to the flotation pulp and it has also been proposed to add the fatty acid to the flnely ground ore and to mechanically admix the same therewith. All of these heretofore proposed methods have certain deleterious features which it is the object of the present invention to eliminate.

In copending application Serial No. 637,542

filed October 12, 1932 by Floyd Weed and Edwin E. Ellis is disclosed a new type of reagent for use in the froth flotation of non-sulfide ores and an improved method of concentrating non-sulfide ores by the use of this reagent.

Floyd Weed, the applicant of the present invention. In applying the teachings of the said copending application to the concentrating of chromite ores certain modifications and improve- 10 ments of the broad invention disclosed therein has been found necessary.

Chromite ores contain chromite (FeCrzOr) associated with varying gangue materials chiefly alumina (A1203), silica (SiOz), magnesia (MgO) and iron oxide (F620: and FeO) in varying amounts.- The proportion of chromite in the ores may vary widely from a small proportion to a large proportion. The present invention is applicable to all chromite ores regardless of the chromite content thereof, the operating difference lying chiefly in the total amount of the reagents that are necessary to add to the ores, as will hereinafter be disclosed.

Heretofore in the art it has been found as above noted that fatty acids and in particular oleic acid evidences a selective affinity for the metal values of non-sulfide ores. The invention of the above identified application briefly stated resides in the addition of the fatty acid or the fatty acid admixed with a reagent beneflciating the segregation of the metal values from the gangue materials of an ore, to the flotation pulp in a colloidally dispersed condition. In this condition the colloidal particles of the fatty acid and/or the beneflciating reagent aflix themselves readily to the suspended ore particles in the pulp and the subsequent froth flotation step thereby is facilitated and the inordinate consumption of these reagents as heretofore experienced is 40 eliminated.

In applying this broad invention to the froth flotation of chromite ores it is found that the following operating steps are essential: V

(1) Grinding the ore to particle size below about 48 mesh.

(2) Classifying the ground ore to reject all oversized particles and to reject all particles classified as slimes.

(3) Conditioning the flotation pulp to prepare 50 it for the froth flotation which includesneutralizing the pulp to a preferred-pH concentration, addition of the colloidally dispersed reagent to the pulp and the admixing of the same, and then acidifying to a preferred acidity for flotation.

The Floyd Weed 5 of the said copending application is identical with (4) Rougher flotation.

(5) Cleaner flotation.

(6) Recovery of concentrate.

Before further disclosing the present invention reference should be made to the accompanying drawing wherein the single figure discloses a flow sheet diagram of the flotation process of the present invention,

The crude ore mechanically concentrated by any of the heretofore devised methods is subjected first to coarse grinding and then is admixed with water and subjected to fine grinding in a ball or rod mill. The fine ground material is first classified to remove all material above about 48 mesh which is returned to the ball or rod mill for further grinding and the material past 48 mesh is further classified to remove the slimes.

I have found that the gangue material being softer than the chromite, slimes to a greater degree than the chromite and that the discarding of the slimes does not cause a loss of more than 3 to 3.5% of the total chromite in the ore. Where the slimes are not removed I have found that such slimes are unselectively collected by the flotation reagents and the concentrate thus collected is therefore of a lower grade than can otherwise be collected with the slimes removed. The presence of the slimes in the flotation pulp moreover interfere with the normal segregation of metal values and gangue having a uniformly inhibiting or hindering effect on both the gangue and the metal values of the ore and markedly increase the amount of flotation reagents necessary to obtain such segregation. It is impractical to use alkaline dispersion agents to eliminate the slimes inasmuch as I have found that to successfully float chromite the flotation pulp must be maintained at an acidity approximating pH 6.0. The desliming of the ground ore may be accomplished mechanically by a bowl type Dorr classifier, by a Dorr thickener or by hydraulic classification,

Following desliming the pulp may be diluted with water to the approximate density found desirable for flotation, which may vary widely depending upon apparatus, capacity, ore characteristics, specific reagents employed and character of water available or the pulp may be only partially diluted, as is desired or convenient. After dilution the pulp should be substantially neutralized by the addition of acid (or alkali). The pH concentration of the pulp on neutralization should be atleast approximately 7.0 (using phenol red or any indicator sensitive within the range). This neutralized pulp is then discharged to the conditioner and the colloidally dispersed reagent is addedthereto at the conditioner intake in the desired quantity,

The colloidally dispersed reagent added preferably comprises oleic acid colloidally dispersed in water containing a small proportion of a water soluble soap compound. Still more preferably the soap compound is comprised of an amine and a fatty acid, and specifically the soap compound is comprised of triethanolamine and oleic acid. In the forming of the preferred and specific colloidally dispersed reagent, oleic acid is slowly added to water (distilled) containing a small proportion of triethanolamine. The triethanolamine reacts with a proportion of the oleic acid in the ratio of 2.7 parts oleic acid to 1 part triethanolamine (by volume) to form a water soluble soap. During the addition of the acid to the water and triethanolamine solution the solu- ,tion is vigorously stirred and aerated. The temperature of the solution should be maintained at approximately 20 to 30 C. for best results. Agitation and aerating should be continued until a dispersion of the desired colloidal character is obtained.

The specific proportions of oleic acid to water to amine may be varied widely without departing essentially from the nature and scope of the present invention. A stable colloidal dispersion dilutable with water may be made using the ingredients in the following proportion:

Per cent (by volume) Oleic acid -l 25.00 Triethanolamine .25 Water (distilled) 74.75

A relatively unstable colloidal dispersion may be made using 97 to 99.5 parts (by weight) oleic acid; .5 to 3 parts (by weight) triethanolamine and a volume of water approximately equal to the volume of the oleic acid.

The choice of these or other colloidal dispersions rests with the operator and no different operating result will be obtained as long as the oleic acid is in a colloidally dispersed condition at the time of addition to the neutralized pulp. It is apparent, however, that with the higher concentrated colloidal dispersions a less volume of the reagent may be added to the pulp, the ultimate total consumption of reagent depending primarily upon the total chromite content of the ore.

Accordingly with a chromite ore averaging approximately 50% chromite I have found that the total consumption of oleic acid for a rougher separation by froth flotation should approximate .3 pounds per ton of ore. This quantity of oleic acid must or may be added as a colloidal dispersion of any specific concentration.

With a chromite ore averaging approximately 50% chromite I have found that the total consumption of oleic acid for a rougher separation by froth flotation should approximate .3 pounds per ton of ore.

The density of the pulp subjected to rougher flotation may be varied within rather wide, limits and depends somewhat upon the total per cent of chromite in the ore and in part upon the type of associated mineral impurities.

The presence or absence of froth modifying agents and the quantities thereof also are dependent upon the quantity of and type of associated mineral impurities and the density of the pulp as well as the specific metal salts in solution in the water of the pulp. I have found that pine oil and/or cresylic acid may be used with most ores and that they each beneficiate the froth sufficiently to facilitate the segregation of the chromite from the gangue.

With chromite ores averaging about 50% chromite and having serpentine quartz, peridotite and mica as associated mineral impurities I have found that .03 to .05 pounds per ton of ore of pine oil or .05 to .07 pounds per ton of ore of cresylic acid may be added with beneficial results upon the segregation of the metal values of the ore from the gangue.

Conditioning of the pulp comprises substantially thorough intermingling or admixing of the substantially neutral pulp with the added colloidally dispersed reagent. This may be .done in a number of ways but preferably by mechanical agitation. The temperature of the pulp during the conditioning does not appear to affect either the conditioning or the subsequent flotation of the ore, good results having been obtained in each case where the temperature of the pulp approximated 10 C. which is below the melting point of the oleic acid reagent.

Following conditioning the pulp is acidified to a pH concentration of approximately 6.0 and transferred to a flotation cell where a rougher concentrate is separated. Any type of mechanically agitated flotation cell may be used. The chromite bearing froth rises to the surface and may be skimmed off by any well known method. The tailings may contain some chromite which may be recovered therefrom by gravity methods. Prior to such recovery any flocculation of the chromite must be broken down by acid or alkali additions.

The rougher concentrate can be cleaned by repeating the froth flotation in the same or a similar flotation cell. The rougher concentrates are made up into a pulp of a desired density (approximately 10% solids) and the acidity of the solution should be adusted to a pH concentration approximating 5.0 to 5.5. An amount of colloidally dispersed oleic acid reagent and/ or froth modifying agent such as pine oil, cresylic acid, etc. may be added to the pulp to facilitate the cleaner flotation.

The cleaner concentrate may be filtered and/or dried in any desired manner. The tailings from the cleaner concentration may be reground and returned to the flotation circuit either to the conditioning cell or put through the desliming classifier as indicated.

By returning reclaimed water to the circuit the acid consumption of the present process will be greatly reduced. It is deterrnlned that the tailings water shows only about .1 to .2 bf a pH unit less acid than does the water at the start of flotation. The amount of reclaimed water that may be returned and the point at which it may be returned will be controlled by the acidity and/or alkalinity of the make up water and the requirements of the circuit.

As an alternative process I disclose in the flow sheet the use of two rougher flotation cells connected in series with the rougher concentrate feeding into a single cleaner flotation cell. It is apparent, however, that anyesuch arrangement of rougher cells would depend primarily upon relative capacities of rougher and cleaner cells and relative proportions of rougher concentrates obtained and that such modifications or arrangements as are essential for the economic operation of the present invention are included within the scope thereof.

Having broadly and specifically defined the nature and scope of the present invention it is apparent that many modifications and departures may be made from the specific embodiments disclosed herein without substantially departing from the scope of the same as may be included within the following claims.

What I claim is:

1. The method of concentrating chromite ores which comprises forming a crude concentrate of the chromite ore, grinding the same to a particle size less than about 48 mesh, classifying the ground ore to reject oversize particles and particles of a size known as slimes, suspending the classified ore in water to form a flotation pulp, neutralizing the pulp to a pH concentration approximating 7.0, incorporating therein a proportion of oleic acid colloidally dispersed in water containing a proportion of a water soluble soap compound, acidifying the pulp to a pH concentration approximating 8.0, and thereafter aubjecting the pulp to froth flotation.

2. The method of concentrating chromite ores which comprises forming a crude concentrate of the chromite ore, grinding theme to a particle Y 5 size less than about 48 mesh, classifying the ground ore to reject oversize particles and particles of a size known as slimes, suspending the classified ore in water to form a flotation pulp,- neutralizingthe pulp to a pH concentration approximating 7.0, incorporating therein a proportion of oleic acid colloidally dispersed in water containing a proportion of triethanolamine, acidifying the pulp to a pH concentration approximating 6.0, and thereafter subjecting the pulp to 15 froth flotation. v

3. In the froth flotation of chromite ores, the steps of neutralizing the flotation pulp, adding thereto oleic acid colloidally dispersed in a water solution of an amine soap compound, and there 20 after acidifying the pulp before subjecting the pulp to flotation.

4. The method of concentrating chromite ores which comprises grinding said chromite ores, suspending the ground ore in water to form a flota- 25 tion pulp, neutralizing said pulp, incorporating therein a proportion of a fatty acidcolloidally dispersed in water containing a proportion of an alkyl amine soap compound, acidifying the pulp and thereafter subjecting the acidified pulp to 30 froth flotation.

5. The method of concentrating chromite ores which comprises grinding said chromite ores, suspending the ground ore in water to form a flotation pulp, neutralizing said pulp, incorporating 35 therein a proportion of a fatty acid colloidally dispersed in an aqueous solution of an alkyl amine soap compound, adding thereto'a proportion of a froth modifying agent, acidifying the pulp and thereafter subjecting the acidified pulp to froth 40 flotation.

6. The method of concentrating chromite ores which comprises grinding said chromite ores, classifying the ground ore to a preferred range of particle size, suspending the ore in water to form a flotation pulp of a desired density, neutralizing the pulp, incorporating therein a proportion of oleic acid colloidally dispersed in an aqueous solution of an alkyl amine soap compound, acidifying the pulp and thereafter subjecting the pulp to 50 froth flotation.

7. The method of concentrating chromite ores which comprises grinding said chromite ores, classifying the ground ore to a preferred range of particle size, suspending the ore in water to form a flotation pulp of a desired density, neutralizing the pulp, incorporating therein a proportion of an oleic acid colloidally dispersed in an aqueous solution of an alkyl amine soap compound, adding thereto a proportion of a frothing agent, acidifying the pulp, and thereafter subjecting the pulp to froth flotation.

8. The method of concentrating chromite ores which comprises mechanically concentrating the crude chromite ore, grinding the crude ore concentrate, classifying the ground ore to remove oversize particles and slimes, suspending the classified ore in water to form a flotation pulp;

which comprisesmechanically concentrating the 75 crude chromite ore, grinding the crude ore concentrate, classifying the ground ore to remove oversize particles and slimes, suspending the classified ore in water to form a flotation pulp, neutralizing the pulp, incorporating therein oleic acid colloidally dispersed in water containing triethanolamine, adding thereto a proportion of a frothing agent, acidifying the pulp to a pH concentration approximating 6.0, and thereafter subjecting the pulp to froth flotation.

10. The method of concentrating chromite ores which comprises forming a crude concentrate of the chromite ore, grinding the same to a particle size less than about 48 mesh, classifying the ground ore to reject oversize particles and particles of a size known as slimes, suspending the classified ore in water to form a flotation pulp, neutralizing the pulp to a pH concentration approximating 7.0, incorporating therein a proportion of a reagent comprised in part of a fatty acid and in part of pine oil colloidally dispersed in an aqueous solution of a fatty acid-alkyl amine soap compound, acidifying the pulp to a pH concentration approximating 6.0, and thereafter subjecting the pulp to froth flotation.

11; The method of concentrating chromite ores which comprises forming a crude concentrate of the chromite ore, grinding the same to a particle size less than about 48 mesh, classifying the ground ore to reject oversize particles and particles of a size known as slimes, suspending the classified ore in water to form a flotation pulp, neutralizing the pulp to a pH concentration approximating 7.0, incorporating therein a proportion of a reagent comprised in part of oleic acid and in part of pine oil colloidally dispersed in an aqueous solution of a fatty acid-alkyl amine soap compound, acidifying the pulp to a pH concentration approximating 6.0, and thereafter subjecting the pulp to froth flotation.

12. The method of concentrating chromite ores which comprises forming a crude concentrate of the chromite ore, grinding the same to a particle size less than about 48 mesh, classifying the ground ore to reject oversize particles and particles of a size known as slimes, suspending the classified ore in water to form a flotation pulp, neutralizing the pulp to a pH concentration approximating 7.0, incorporating therein a proportion of oleic acid and cresylic acid colloidally dispersed in a fatty acid-alkyl aqueous solution of an amine soap compound, acidifying the pulp to a pH concentration approximating 6.0, and thereafter subjecting the pulp to froth flotation.

13. The method of concentrating chromite ores which comprises forming a crude concentrate of the chromite ore, grinding the same to a particle size less than about 48 mesh, classifying the ground ore to reject oversize particles and particles of a size known as slimes, suspending the classified ore in water to form a flotation pulp, neutralizing the pulp to a pH concentration approximating 7.0, incorporating therein a proportion of oleic acid and linseed oil colloidally dispersed in an aqueous solution of a fatty acid-alkyl amine soap compound, acidifying the pulp to a pH concentration approximating 6.0, and thereafter subjecting the pulp to froth flotation.

14. The method of concentrating chromite ores which comprises forming a crude concentrate of the chromite ore, grinding the same to a particle size less than about 48, mesh, classifying the ground ore to reject oversize particles and particles of a size known as slimes, suspending the classified ore in water to form a flotation pulp,

neutralizing the pulp to a pH concentration approximating 7.0, incorporating therein a proportion of a reagent consisting of oleic acid and linseed oil colloidally dispersed in water containing a proportion of triethanolamine, acidifying the 5 pulp to a pH concentration approximating 6.0, and thereafter subjecting the pulp to froth flotaion.

15. In the froth flotation of chromite ores, the step of incorporating within the flotation pulp a 1 proportion of a fatty acid, said acid being incorporated as colloidal sized particles dispersed in an aqueous solution of an alkyl amine soap compound.

16. In the froth flotation of chromite ores, the 15 step of incorporating within the flotation pulp a proportion of a reagent comprised in part of a fatty acid and in part of an oil, said reagent being incorporated as colloidal sized particles dispersed in an aqueous solution of an alkyl amine soap 20 compound.

17. In the froth flotation of chromite ores, the. step of incorporating within the flotation pulp a proportion of oleic acidcolloidally dispersed in an aqueous solution of an alkyl amine soap com- 25 pound. K

18. In the froth flotation of chromite ores, the step of incorporating within the flotation pulp a proportion of a reagent comprised of oleic acid and linseed oil colloidally dispersed in an aque- 30 ous solution of an alkyl amine soap compound.

19. In the froth flotation of chromite ores, the method of incorporating within the flotation pulp the fatty acid evidencing a selective aflinity for the chromite which comprises first forming a 001- 35 loidal dispersion of said acid in an aqueous solution of an alkyl amine soap compound, forming a pulp of the desired physical and chemical characteristics and then adding the colloidal dispersion to the flotation pulp. 40

20. In the froth flotation of chromite ores the method of incorporating within the flotation pulp the fatty acid evidencing a selective aiflnity for the chromite and a frothing agent; which comprises first admixing the fatty acid and said 45 frothing agentin their desired relative proportions, colloidally dispersing the admixture in an aqueous solution of an alkyl amine soap compound, forming the ore into a flotation pulp of the desired physical and chemical characteristics, 5 and then adding the colloidal dispersion to the said pulp.

21. In the froth flotation of chromite ores, the steps of neutralizing the flotation pulp, adding thereto a proportion of a fatty acid colloidally 55 I dispersed in an aqueous solution of an alkyl amine soap compound, and thereafter acidifying the pulp before subjecting the pulp to agitation and aeration to form a minerals containing froth.

22. In the froth flotation of chromite ores, the 60 steps of adding'to a neutral pulp a proportion of a reagent comprised in part of oleic acid and in part of a frothing agent colloidally dispersed in an aqueous solution of an alkyl amine soap compound, and thereafter acidifying the pulp before subjecting the pulp to agitation and aeration to form a minerals containing froth.

23. In the froth flotation 0f chromite ores, the steps of adding to a neutral pulp a proportion 70 of a reagent comprised in part of oleic acid and in part of pine oil colloidally dispersed in an jecting the pulp to agitation and aeration to form a minerals containing froth.

24. The method of concentrating chromite ores which comprises neutralizing a flotation pulp containing said ore, incorporating therein a proportion of a fatty acid. colloidally dispersed in a solution consisting of water and an alkyl amine soap compound, acidifying said pulp, agitating and aerating said pulp to form a chromite containing froth and separating the said froth.

25. The methodof concentrating chromite ores which comprises neutralizing a flotation pulp containing said ore, incorporating therein a proportion of a fatty acid colloidally dispersed in a solution consisting of water and an alkyl amine soap compound, incorporating also a proportion of a froth modifying agent, acidifying said pulp, agitating and aerating said pulp to form a chromite containing froth and separating the said froth.

26. The method of concentrating chromite ores which comprises neutralizing a flotation pulp containing said ore, incorporating therein a proportion of a colloidal dispersion comprised of a mixture of a fatty acid and pine oil emulsified in a solution consisting of water and an alkyl amine soap compound, acidifying said pulp, agitating and aerating said pulp to form a chromite containing froth and separating the said froth.

27. The method of concentrating chromite ores which comprises neutralizing a flotation pulp containing said ore, incorporating therein a proportion of a mixture of oleic acid and pine oil colloidally dispersed in an aqueous solution of an alkyl amine soap compound, acidifying said pulp,

agitating and aerating saidpulp to form a chromite containing froth and separating the said froth.

28. The method of concentrating chromite ores which comprises neutralizing a flotation pulp containing said ore, incorporatingtherein a proportion of a fatty acid colloidally dispersed in a solution consisting of water and an alkyl amine soap compound, acidifying said pulp to a pH concentration of approximately 6.0, agitating and aerating said pulp to form a chromite containing frothand separating the-said froth.

29. The method of concentrating chromite ores which comprises neutralizing a flotation pulp containing said ore, incorporating therein a proportion of a fatty acid colloidally dispersed in a solution consisting of water and an alkyl amine soap compound, acidifying said pulp to a pH concentration of approximately 6.0, mechanically agitating the pulp to thoroughly disseminate the oleic acid and pine, oil therethrough, agitating and aerating said pulp to form a chromite containing froth and separating the said froth.

30. The method of concentrating chromite ores which comprises neutralizing a flotation pulp containing said ore, incorporating therein a proportion of a fatty acid colloidally dispersed in a solution consisting of water and an alkyl amine soap compound, acidifying said pulp, thoroughly disseminating the said acid throughout the pulp, agitating and aerating said pulp to form a chromite containing froth and separating the said froth.

FLOYD WEED. 

